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Bending of Sheet Metals
Published in Kakandikar Ganesh Marotrao, Anupam Agrawal, D. Ravi Kumar, Metal Forming Processes, 2023
The formation of precipitates or presence of other second phase particles may improve the strength of the alloys but have detrimental effect on ductility, formability, and bendability [6, 36]. The presence of these secondary phases lead to void formation at the particle-matrix interface as a result of strain localization. When large particles are formed at the grain boundary, the fraction of alloying element in matrix reduces near the grain boundary. This lead to the reduction in strength of the material adjacent to the grain boundary as compared to the grain interior. Moreover, the presence of large particles reduces the cohesive bond between two adjacent grains. This can promote grain boundary fracture during bending [40]. With the increased amount of particles at the grain boundary, de-cohesion of boundary becomes dominant fracture mechanism under bending for agehardenable alloys. In addition to this, ductile fracture of grain boundary can occur at the later stage of the bending due to the strain localization and can be viewed on the fractured surface in the form of microdimples. The void formation can also occur due to the breakage of particles under high strain [28]. While the large particle results in formation of crack, the growth and propagation is further influenced by the shape of the small precipitates present in the grain boundary [29]. Small amount of nano particle addition can have detrimental effect on bending while have almost no effect of tensile elongation [6].
Nanomaterials and Its Application as Biomedical Materials
Published in Savaş Kaya, Sasikumar Yesudass, Srinivasan Arthanari, Sivakumar Bose, Goncagül Serdaroğlu, Materials Development and Processing for Biomedical Applications, 2022
G.S. Mary Fabiola, P. Dhivya, M. Anto Simon Joseph
Mechanical properties of metals are often associated with mechanical characteristics of metal which include strength, toughness, hardness, brittleness, plasticity, elasticity, rigidity, malleability, and ductility. The traditional inorganic metals are brittle, hard, and rigid but lack plasticity and elasticity. Alternatively, organic materials are flexible but are not rigid, brittle, and strong. These disadvantages are overcome by the nanomaterials which possess high surface area, volume, and quantum effects when compared to micro- and macroscopic materials. The influence of the selection of nanomaterials, the process of fabrication, grain size, and structure of the grain boundary has a noteworthy effect on the mechanical properties of nanomaterials. In comparison with the bulk, nanomaterials refine the grain size and form inter/intragranular structure, improving the grain boundary and thereby enhancing the mechanical properties of nanostructured materials. The flexural strength of nano-Al2O3 ceramics is comparatively stronger when compared with micro-scale monolithic alumina ceramics (Teng et al. 2007).
Nanostructuring of Materials by Severe Deformation Processes
Published in Amit Sachdeva, Pramod Kumar Singh, Hee Woo Rhee, Composite Materials, 2021
Aman J. Shukla, Devesh K. Chouhan, Somjeet Biswas
In order to be in the BNM category, an auxiliary requirement is the homogeneous distribution of nanoscale elements in the whole sample. NS materials exhibit other structural elements that are in the nanometer range, i.e., second phase particles, precipitates, nanosized twins, substructures, etc. These structural elements have a significant effect on the properties of the materials. For example, the microstructure of SPD-processed metals/alloys includes grain boundaries, which may form equilibrium, nonequilibrium, random, low-angle, and high-angle boundaries with special characteristics [15] depending on the processing techniques used. Moreover, the different characteristics of the boundary may have different mechanisms of transportation, i.e., diffusion, etc. These grain boundary properties lead to different mechanical, chemical, magnetic, and electrical properties. The various SPD techniques used in the formation of NS materials may give a platform for new advancement in the enhancement of mechanical properties such as strength and ductility, leading to new structural and functional applications of the materials.
Active screen plasma nitriding of laser powder bed fusion processed 316L stainless steel for the application of fuel cell bipolar plates
Published in Virtual and Physical Prototyping, 2023
Kaijie Lin, Jingchi Qiao, Dongdong Gu, Haoran Wang, Bo Shi, Wanli Zhang, Junhao Shan, Yong Xu, Linhai Tian
Prior studies indicated that grain size can affect the formation of nitrided layer. The decreased grain size leads to the increase of grain boundary density. As the interface between adjacent grains, the atom arrangement and structure of grain boundaries are irregular and loose. This characteristic would reduce the resistance of nitrogen diffusion and provide diffusion channels for nitrogen to move inwards from the surface, which also has been proved by Lu et al. (Lu et al. 2021). As discussed before, the grain size of LPBF-2 was smaller than that of Wrought. This may be due to the high cooling rate around 103–108 K/s of the LPBF process, leading to the high degree of supercooling in molten pool, which made the nucleation rate of grain higher than the growth rate, thus realising grain refinement (Sabzi et al. 2020). Therefore, comparing with Wrought-316L SS, the smaller grain size of LPBF-processed 316L SS facilitated the nitrogen diffusion (Figure 13c). (iv) Multi-layers level: The formation of columnar grain with similar orientation
Corrosion behaviour of compositionally modulated nanocrystalline Ni–W coatings
Published in Surface Engineering, 2020
Nitin P. Wasekar, S. Gowthami, A. Jyothirmayi, J. Joardar, G. Sundararajan
In principle, the nanocrystalline metals/coatings represent higher fraction of intercrystalline volume (i.e. grain boundaries and triple junctions) [26]. Therefore, the nanocrystalline materials are in higher energy state and are active due to the large grain boundary area. As a consequence, the electrochemical electron transfer and diffusion rates are higher compared to their bulk counterparts. An implication of this results in improved rates of oxide formation thereby leading to early passivation effects. The decrease in corrosion current and early passivation with the decrease in grain size (due to an increase in W content of Ni–W alloy) is therefore evident in the present study. As an inspiration of the above fact, the layering of Ni–W alloy with individual W content results in improved corrosion resistance by providing the barrier for electrochemical species to reach the underlying substrate. However, the basic question arises why despite having same tungsten content in the outer layer, Ni15W, Ni(5 + 15)W and Ni(3 + 5+15)W coatings exhibit different anodic behaviour? In general, all other parameters being equal (composition, grain size, surface roughness, texture, etc), the difference in corrosion behaviour can be rationalized based on coating defect (e.g. porosity) and surface residual stress. The individual effect is presented below.
Effect of Gadolinium on the structural and dielectric properties of BCZT ceramics
Published in Phase Transitions, 2020
S. Saparjya, T. Badapanda, S. Behera, B. Behera, Piyush R. Das
The complex impedance spectroscopy (CIS) [39] is a non-destructive and easy method to comprehend the conduction phenomenon and electrical processes in the materials. This method is used to investigate the response of a system in the presence of an alternating field, also the estimation of impedance and associated parameters as a function of temperature and frequency is calculated. This method is furthermore helpful to learn the contributions of (i) bulk/grain effect, (ii) grain boundary effect, and (iii) electrode polarization effect on impedance and other correlated parameters. By using the basic equations [40,41], the real and imaginary components of impedance and associated parameters of the materials can be calculated. With the help of these equations, the complex impedance of the electrode/ceramic/electrode capacitor can be calculated as per the following relation: